Oat has been considered a healthy cereal for a long time. It is rich in not only proteins, amino acids, essential fatty acids, vitamin B complex, and minerals such as iron, zinc and magnesium, but also water soluble and non-water soluble dietary fibers, especially β-glucan. Many medical or nutritional research papers have shown that oat β-glucan has the effect of preventing or alleviating cardiovascular diseases, diabetes, hypertension or constipation. Therefore, the nutrients in oat have been used as additives of various food products.
U.S. Pat. No. 4,996,063 discloses a method for producing a water-soluble dietary fiber composition by treating oat with α-amylase. The resultant powdered dietary fibers can be used as food additives and fat substitutes.
U.S. Pat. No. 5,686,123 discloses a homogenous and stable cereal suspension and the method of making the same, which comprises grinding rolled oats to a particle size of 0.8 to 1 mm, adding water having the temperature of 50 to 53° C. with agitation to form an oat slurry, treating the suspension with β-amylase to a viscosity of 3 to 0.1 Pas in the first enzyme treatment step, further treating the suspension with α-amylase to a viscosity of <0.5 Pas in the second enzyme treatment step, and subjecting the suspension to Ultra High Temperature (UHT) at the temperature of 137 to 138° C. for 3 to 4 seconds to obtain a homogenous and stable oat suspension.
U.S. Pat. No. 6,451,369 discloses a non-dairy, ready-to-use milk substitute and products made therewith. It discloses a method which comprises the steps of wet-milling oats to provide a pre-gelatinized suspension having a dry solids content of 10 to 15% w/w, and adding α-amylase and β-amylase simultaneously for hydrolysis of 1 to 2 hours to provide an oat suspension containing a significant amount of maltose and β-glucans.
U.S. Pat. No. 6,685,974 discloses a process for preparing an oat-based functional syrup, comprising the steps of blending an oat material having a granulation of less than #100 mesh (corresponding to 150 μm) with water to form a slurry, adding α-amylase to proceed an enzymatic treatment (68° C. for 2.5 hours), adding glucoamylase enzyme to proceed a further enzymatic treatment, and cooking the slurry to convert the slurry into an oat-based functional syrup. However, the product prepared with the process is substantially flavorless.
Furthermore, CN Patent Publication No. 1566161 discloses a process for preparing oat β-glucan, which comprises the steps of (1) preparing oat bran from oat, eradicating enzymes, (2) watering and stiffing at the temperature of 45-65° C., adjusting the pH value to 9-11, (3) separating and gathering filter liquor, charging alpha-amylase for processing, retaining 1-2 hours at 70-90° C., (4) cooling down to 10-30° C., adjusting the pH value to 4.5-5.0, agitating and stewing, settling proteins, (5) centrifuging to obtain the supernatant fluid, hyperconcentrating, charging alcohol isopropylicum into the concentration liquid, obtaining beta-gluglucosan gelatineous deposition, and (6) centrifuging the beta-gluglucosan gelatineous deposition, vacuum drying to obtain the beta-gluglucosan gelatineous end product.
In addition, CN Patent Publication No. 1966531 discloses a process for preparing oat β-glucan which comprises the steps of using oat bran as raw materials, crushing, microwave-assisted-extracting, adding amylase and glucoamylase, isoelectric-point-precipitating, centrifugating and separating, concentrating the supernatant, precipitating with ethanol, centrifugating and collecting the precipitation, solving with water, hydrolyzing with beta-glucanase, and spray-drying process to obtain the high-efficiency prebiotics oat β-glucan with enhanced intestinal and fecal bifidobacteria and actobacillus value-added effect.
Although the methods for preparing water soluble dietary fibers disclosed in the prior art can produce oat β-glucan with a high yield, their steps are complicated and involve enzymatic treatments which take a long time, resulting in high production costs. Furthermore, some products of the prior art have lost the natural flavor and aroma of oats and cannot provide the flavor of natural oats when consumed.
In addition to oat β-glucan, isomalto-oligosaccharide is known to lower the pH value of the intestine and enhance bowl movements. Isomalto-oligosaccharide can also inhibit the proliferation of harmful bacteria and decrease the toxic wastes generated in the metabolism of harmful bacteria, so it has the intestinal cleansing effect, and can vitalize bodily functions. However, the processes of the prior art do not provide an oat-based drink rich in both β-glucan and isomalto-oligosaccharide.
Accordingly, the present invention provides a process that combines micronized milling technique and enzymatic hydrolysis, wherein rolled oats are micronized and subjected to two-stage enzymatic treatments with α-amylase, and β-amylase and trans-glucosidase. In accordance with the invention, a homogenous, stable oat-based functional drink rich in β-glucan and isomalto-oligosaccharide can be produced.